Structures such as copying machines, faxes, and printers are constructed such that a plurality of members are assembled, and then these members are mutually fastened by means of fastening such as welding, screw fastening, riveting, etc.
Since welding is carried out by melting members, the welded portion shows high strength. However, the welding requires large scale equipment, so it is disadvantageous of increasing cost. It also has a problem of deterioration of accuracy by thermal deformation. Consequently, sometimes screw fastening and rivet fastening can be used instead of using the welding.
Generally, when two members are mutually fastened by using a screw or rivet, a hole diameter in which the screw or rivet is inserted is adopted to be larger than the outer diameter of the inserted portion of the screw or the rivet; therefore, ample room is assured between the inserted portion and the hole when the screw or rivet is inserted. This is because the cost increase by the increase in diameter accuracy is curved by adopting the rivet or screw to be easily inserted.
However, in the screw fastening or rivet fastening, if ample room is maintained to the hole diameter, a space corresponding to the ample room is left after fastening. Accordingly, there was a problem that the connected portion is misaligned when large load is applied to the connected portion.
In order to solve the above problem the applicant has proposed a new fastening method described in Japanese Patent Laid-Opens H-10-299735, H10-306813, and H10-306814.
More particularly, the applicant has provided a blind rivet. In such a blind rivet, the mandrel of the blind rivet and the inside of the body to accept the rivet are respectively formed with a bump, and the bump of the mandrel is radially expanded so as to increase the outer diameter toward the bump of the body in the fastening process, so that the space between the mandrel and the inside of the body, which has been generated after fastening, is eliminated, and both members to be mutually connected by the blind rivet can be fastened without generating change in the relative positions over time.
However, the above blind rivet has a particular shape, so that it was disadvantageous in that the manufacturing cost is high.